AI 中文总结
本研究展示了由锗双量子点空穴自旋构成的简并单重态-三重态量子比特，利用全电方式独立调控交换相互作用与塞曼能差，实现正交旋转，单量子比特门保真度达99.53%，为多量子比特规模化提供了途径。
AI 中文摘要
单重态-三重态量子比特为半导体量子计算提供了一种极具吸引力的编码方式，兼具无需辅助量子比特的读出能力、对共模噪声的低敏感性以及基带电压控制的优势。然而，塞曼能差ΔE_Z通常由局域磁场梯度或g因子不均匀性固定，使得交换相互作用J成为唯一可动态调控的参数。这种始终存在的ΔE_Z会阻碍量子比特旋转轴的正交控制，并在空闲期间引入不必要的态旋转。本文中，我们展示了由锗双量子点中的两个空穴自旋构成的简并单重态-三重态（DST）量子比特的全电正交控制。利用两个自旋的电可调各向异性g因子，我们确定了一个ΔE_Z和J均为零的区域，使S和T0态在空闲点处简并。仅通过施加基带电压脉冲，我们可独立控制J和ΔE_Z，实现完全正交的Z轴和X轴旋转。随机基准测试显示，在约100纳秒的门持续时间下，平均物理单量子比特门保真度达99.53%。最后，我们在宽范围的磁场取向中电调谐简并点，使其能在相干时间增强的区域工作，并为在共享全局磁场下实现多量子比特规模化提供了途径。
英文摘要
Singlet-triplet qubits offer an attractive encoding for semiconductor quantum computing, combining ancilla-free readout, reduced sensitivity to common-mode noise, and baseband voltage control. However, the Zeeman energy difference $ΔE_\mathrm{Z}$ is typically fixed by local magnetic field gradients or $g$-factor inhomogeneities, leaving the exchange interaction $J$ as the only dynamically tunable parameter. This always-on $ΔE_\mathrm{Z}$ precludes orthogonal control of the qubit's rotation axes and introduces unwanted state rotations during idling. Here we demonstrate all-electrical orthogonal control of a degenerate singlet-triplet (DST) qubit formed by two hole spins in a germanium double quantum dot. Exploiting the electrically tunable anisotropic $g$-factors of the two spins, we identify a regime where both $ΔE_\mathrm{Z}$ and $J$ vanish, making the $S$ and $T_0$ states degenerate at the idle point. By applying only baseband voltage pulses, we independently control both $J$ and $ΔE_\mathrm{Z}$, enabling fully orthogonal $Z$- and $X$-axis rotations. Randomized benchmarking yields an average physical single-qubit gate fidelity of 99.53\% for a gate duration of approximately 100 ns. Finally, we electrically tune the degenerate point across a wide range of magnetic field orientations, enabling operation in a regime of enhanced coherence time and offering a route towards multi-qubit scaling under a shared global magnetic field.
